Image processing apparatus and method thereof and storing medium

ABSTRACT

An object is to add additional information to an input image using a general image processing without providing a specific information adding section which is not included in a general image processing unit. To attain this object, an apparatus of the present invention inputs M-value image data and converts the inputted M-value image data into N-value image data, wherein the value M is larger than the value N, on the basis of threshold table groups composed of plural kinds of threshold tables of which using order is determined so as to indicate predetermined additional information.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an image processing apparatusfor and method of adding predetermined information to an input image anda storing medium which stores the method.

[0003] 2. Related Background Art

[0004] Conventionally, as an output apparatus for performing a colorprint, a full-color printer, a full-color copying machine, a full-colorfacsimile apparatus or the like is practically used.

[0005] The output apparatus such as a color copying machine, a colorprinter or the like becomes cheaper every year and becomes to be widelyused.

[0006] On the other hand, quality of a printed image of the outputapparatus has been improved. Therefore, it becomes possible to form animage of which quality is same as that of an image of valuablesecurities or the like, where image is generally prohibited to beformed. Consequently, there occurs such fear that the image prohibitedto be formed is illegally formed.

[0007] In order to inhibit thus illegal image formation, conventionally,such a technique as putting predetermined additional informationdifficult to be perceived by human eyes on all images to be formed hasbeen known. For example, in a case where a color image composed ofyellow, magenta, cyan and black components is printed, a printing is tobe performed by adding a dot pattern indicating the additionalinformation to the yellow component. Consequently, the additionalinformation can be extracted upon analyzing the yellow component and thedot pattern of a color image finally printed.

[0008] As the additional information, it is preferable to applyinformation which can easily grasp the image printed condition, forexample, such information as a manufacturing number of copying machine,a manufacturer name or the like.

[0009] By the way, in a technique for adding additional information toan output image in order to chase forgery action, even if the additionalinformation is added by using a color which is the most difficult to beperceived, an extra signal should be added on an image signal.Accordingly, since the added signal acts as a noise to an original imagesignal, there occurs such a problem as deteriorating quality of theoutput image. Especially, in a device which forms an image by performingbinary image formation for each color such as an ink jet printer, thatis, in a device for outputting an image on the basis of an image signalwhich is pseudo halftone processed depending on a dither method, anerror diffusion method or the like, a deterioration of image quality isremarkably found.

[0010] In a case where the additional information is added, the qualityof the output image or detectability of the additional information isdeteriorated in response to a characteristic of a recording medium.Therefore, in a case where the recording medium in a low level of afixing characteristic of a toner is used, it is preferable to add theadditional information under the condition of a high density or a largepattern size as long as possible in order to maintain the detectabilityof the additional information. In a case where the recording medium in ahigh transmittance is used, it is preferable to add the additionalinformation under the condition of a low density or a small pattern sizeas long as possible in order to prevent the deterioration of imagequality. That is, it is desirable to maintain a suitable balance betweenthe quality of the output image and the detectability of the additionalinformation in response to the characteristic of the recording medium.

SUMMARY OF THE INVENTION

[0011] However, in a conventional technique for adding additionalinformation, a specific image processing means, which is different froma general image processing for adding the additional information, has tobe provided. As a result, there has been a possibility of requiring alarge cost for an apparatus and performing an image processing which isnot adapted to another image processing such as a dither processing orthe like.

[0012] The present invention is applied in consideration of theabove-mentioned conventional example, and an object is to effectivelyadd the additional information to an input image by utilizing thegeneral image processing without executing the specific imageprocessing.

[0013] More particularly, an object is to effectively add the additionalinformation to the input image by utilizing N-value generation means forN-value generating a multi-value image.

[0014] To attain the above-mentioned object, according to a preferableembodiment of the present invention, an image processing apparatus ofthe present invention comprises input means for inputting M-value imagedata and N-value generation means for converting the M-value image datainputted by said input means into N-value image data, wherein the valueM is larger than the value N, on the basis of threshold table groupscomposed of plural kinds of threshold tables of which using order isdetermined so as to indicate predetermined additional information.

[0015] The present invention maintains to attain the above-mentionedobject, and still another object is to add the additional informationdepending on the most suitable forming pattern in accordance with thekind or characteristic of a recording medium.

[0016] To attain the above-mentioned object, according to a preferableembodiment of the present invention, the image processing apparatus ofthe present invention further comprises detection means for detectingthe kind of a recording medium on which an image indicated by theM-value image data inputted by said input means is to be formed, whereinsaid N-value generation means controls whether the N-value generation isperformed or not to the M-value image data on the basis of the thresholdtable groups in accordance with the kind of the recording medium.

[0017] Other objects and features of the present invention will becomeapparent from the following embodiments and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 indicates an example of a threshold table used in a firstembodiment;

[0019]FIG. 2 indicates an example of a threshold table used in the firstembodiment;

[0020]FIG. 3 indicates bit information of coordinate information in animage in the first embodiment;

[0021]FIG. 4 indicates areas, to which additional information is added,in an input image;

[0022]FIG. 5 indicates an operation procedure of a pseudo halftoneprocessing in the first embodiment;

[0023]FIG. 6 indicates an example of a threshold table used in a secondembodiment;

[0024]FIG. 7 indicates an example of a threshold table used in thesecond embodiment;

[0025]FIG. 8 indicates areas, to which additional information is added,in an input image;

[0026]FIG. 9 indicates the state of a plurality of thresholds used bycombining each other;

[0027]FIG. 10 indicates an operation procedure of a pseudo halftoneprocessing in the second embodiment;

[0028]FIG. 11 indicates bit information of coordinate information in animage in the second embodiment;

[0029]FIG. 12 indicates an example of a threshold table used in a thirdembodiment;

[0030]FIG. 13 indicates an example of a threshold table used in thethird embodiment;

[0031]FIGS. 14A and 14B indicate an example of a system constructionhaving an image processing unit;

[0032]FIG. 15 indicates the state of assigning threshold tables withinan additional area;

[0033]FIG. 16 is a block diagram showing the structure of an LBP (laserbeam printer);

[0034]FIG. 17 is a conceptional view showing a structural example of theLBP;

[0035]FIG. 18 is a block diagram showing a structural example of aprinter controller;

[0036]FIG. 19 is a flow chart showing an example of procedure ofgenerating a video signal and transmitting it depending on the printercontroller;

[0037]FIG. 20 is a flow chart showing an example of processing procedurefor adding additional information to an image to chase a forgery;

[0038]FIG. 21 indicates an example of thresholds corresponding to eachpixel in 8×8 pixels;

[0039]FIG. 22 indicates an example of a threshold table in which theadditional information is put;

[0040]FIG. 23 indicates a positional example of area to which theadditional information on an image is added;

[0041]FIG. 24 indicates an assigning example of information according toa column position in coordinate information;

[0042]FIG. 25 indicates an assigning example of information according tothe column position in the coordinate information;

[0043]FIG. 26 is a flow chart showing an example of density processingfor a designated X-Y coordinate;

[0044]FIG. 27 is a flow chart showing an example of procedure ofgenerating a video signal and transmitting it depending on the printercontroller in a fifth embodiment;

[0045]FIG. 28 is a flow chart showing an example of procedure forselecting the additional information in accordance with a characteristicof a recording medium;

[0046]FIG. 29 indicates an example of an table in which data giving thecharacteristic of the recording medium is registered;

[0047]FIG. 30 indicates a corresponded example between the kind of arecording medium and a pattern of the additional information; and

[0048]FIG. 31 indicates a corresponded example between the kind of arecording medium and a pattern of the additional information.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] As to a pseudo halftone processing described in each embodiment,the present invention includes at least two cases. One case (case shownin FIG. 14A) is that an image processing unit in an unity copyingmachine (particularly, a copying machine 1400 of an electrophotographicsystem), which has a scanner and a printer in a body of equipment,performs the pseudo halftone processing. The other case (case shown inFIG. 14B) is that an image processing unit in a printer (particularly,an LBP 1401 of the electrophotographic system), which performs a printfrom a printer unit after developing color image data described by apredetermined description system inputted from an external host computer1402, performs the pseudo halftone processing. The above-mentionedprinter can be applied to an ink jet printer, a heat sensitive (thermal)printer or the like.

[0050] More particularly, in the case shown in FIG. 14A, an original isread by the scanner to generate multi-value image data to which an imageprocessing (described later) is executed, thereafter, an image isprinted out from the printer as a visible image. On the other hand, inthe case shown in FIG. 14B, the image processing unit inputs code dataof page description language which indicates a multi-value image fromthe host computer 1402 to develop the code data for generatingmulti-value image data to which an image processing (described later) isexecuted, thereafter, an image is printed out from the printer as avisible image.

[0051] In the image processing unit as in the above-mentioned structure,when predetermined additional information is added, in the former case,it is preferable to apply a manufacturing number of a main body of thecopying machine, an ID of user who purchases the copying machine or thelike as the additional information. In the latter case, it is preferableto apply a network ID in an external host computer, a manufacturingnumber, a manufacturer name, an user ID of the host computer, anapplication name being had by the host computer, a version of theapplication, a manufacturing number of a main body of the printer, anuser ID or the like as the additional information.

[0052] Accordingly, in a case where a printed image is illegally used,it becomes possible to know the state of being formed the printed imageby obtaining the additional information to analyze contents of theprinted image.

[0053] The present invention includes the case for simultaneously addingthe above plural items as the additional information.

[0054] In the following embodiment, it is described that binary imagedata is generated depending on the pseudo halftone processing (screeningprocess). However, the present invention is not limited to this, but canbe applied to a case for converting M-value image data into N-valueimage data, wherein the value M is larger than the value N.

[0055] In the following, a system for adding the additional informationunder the condition that the image processing unit shown in FIGS. 14Aand 14B executes the pseudo halftone processing for the inputted imagedata will be described in detail.

[0056]FIGS. 1 and 2 indicate threshold tables used in case of pseudohalftone processing the inputted multi-value image data (8 bits) as thebinary image data.

[0057] In a first embodiment, the additional information is expressedaccording to a switching manner of the threshold table used ingenerating a pseudo halftone image. That is, the threshold tables shownin FIGS. 1 and 2 used in generating the pseudo halftone image (imageafter performing a dither processing) are switched so as to indicatecertain additional information. As a result, the pseudo halftone imagehaving different pixel growing patterns is formed. Consequently, if theswitching manner of the threshold tables is analyzed, from the pseudohalftone image, the additional information put on this image can beextracted.

[0058] It is assumed that each of the threshold tables shown in FIGS. 1and 2 has the size of 8×8 pixels and the dither processing issequentially executed to the inputted image data.

[0059] In this embodiment, in a case where the threshold table shown inFIG. 1 is used, 0 is indicated. In a case where the threshold tableshown in FIG. 2 is used, 1 is indicated. Accordingly, the additionalinformation of one bit can be put on every area of 8×8 pixels in animage. In this embodiment, if the additional information to be added isdata of 16 bits, an area corresponding to the threshold tables of 16pieces is required. Therefore, for example, in a case where theadditional information is added to an image having the sizecorresponding to 16×100 threshold tables, the same additionalinformation is repeatedly added 100 times.

[0060] It should be noted that an expressing manner of the additionalinformation is not limited to this manner, but may be expressed, withouttreating one bit information of 0 or 1 indicated by the threshold tablesshown in FIGS. 1 and 2 as a part of the additional information as it is,by the manner of run-length using the combinations of 0 and 1.

[0061] In this embodiment, an area for putting the additionalinformation on an image of one frame is not limited to an entire image,but an area other than an area to which the additional information isadded at a fixed period (area for switching the threshold tables shownin FIGS. 1 and 2) may be assigned. In the following, a case for usingthis method will be described.

[0062]FIG. 4 indicates the state of assigning manner of theabove-mentioned additional area in this embodiment.

[0063] In FIG. 4, areas of oblique lines are additional areas. That is,the additional information (in this embodiment, 16 bits) has to be puton these areas by switching the threshold tables shown in FIGS. 1 and 2.

[0064] The additional area has the size of containing j×k thresholdtables (in this embodiment, j=4 and k=4). That is, each of theadditional areas can express the additional information of j×k bits.

[0065] As to the positional relation of each area among the additionalareas, it is assumed that length m and length n in FIG. 4 have distancecapable of containing the threshold tables of 16 pieces (8×16 pixels).

[0066]FIG. 3 indicates the state of a bit column indicating a coordinatein each pixel of an image in the image processing unit. As mentionedabove, by setting each parameter as a multiplier of 2, a coordinatevalue expressed in binary number can be easily treated as shown in FIG.3. In FIG. 3, three bits of the lowest order unit (c₂, c₁, c₀) is thecoordinate indicating a position of each of the additional areas. Whentwo bits of upper order (n₃, n₂) within four bits (n₃, n₂, n₁, n₀)adjoining the three bits of the lowest order unit corresponds tospecific values (in this embodiment, n₃=1, n₂=1), since such a thresholdtable as indicating the additional information of 16 bits may have to beselected, it becomes possible to execute a high-speed processing.

[0067] In this embodiment, the threshold table shown in FIG. 1 isunconditionally used to an area other than areas of oblique lines(additional areas) shown in FIG. 4. In this manner, the areas of obliquelines can be easily read.

[0068]FIG. 15 indicates the state of threshold tables Q_(0.0) to Q_(3.3)in each of the additional areas and the state of expressing theadditional information by aligning bit information q_(0.0) to q_(3.3)represented by each of the threshold tables.

[0069] As shown in FIG. 15, the threshold tables of 16 pieces Q_(0.0) toQ_(3.3) are assigned to each of the additional areas. The thresholdtable shown in FIG. 1 or 2 is used for each of these tables Q_(0.0) toQ_(3.3). Therefore, the additional information of 16 bits is expressedby aligning the bit information q_(0.0) to q_(3.3) being the value of 0or 1 represented by the threshold tables Q_(0.0) to Q_(3.3).

[0070]FIG. 5 indicates a procedure for pseudo halftone processing apixel corresponded to coordinates X, Y.

[0071] In a step a2, as to a coordinate value X, it is judged whethereach of n₃ and n₂ is 1 or not. If each of n₃ and n₂ is not 1, the flowadvances to a step a7. If both of n₃ and n₂ are 1, the flow advances toa step a3.

[0072] Next, in the step a3, as to a coordinate value Y, it is judgedwhether each of n₃ and n₂ is 1 or not. If each of n₃ and n₂ is not 1,the flow advances to the step a7. If both of n₃ and n₂ are 1, the flowadvances to a step a4.

[0073] In the step a4, either of bit information q_(0.0) to q_(3.3)corresponding to numerical values n₁ and n₀ of the coordinate values Xand Y are read.

[0074] In a step a5, it is judged whether the bit information q_(0.0) toq_(3.3) which are read are 1 or not. If the judged result does notobtain 1, the flow advances to the step a7. If the judged result obtains1, the flow advances to a step a6.

[0075] In the step a6, it is set to perform the pseudo halftoneprocessing by using the threshold table shown in FIG. 2, that is, thetable of indicating 1. On the other hand, in the step a7, it is set toexecute the pseudo halftone processing by using the threshold tableshown in FIG. 1, that is, the table of indicating 0.

[0076] In a step a8, density information (pixel value) of the coordinatevalues X and Y is compared with the thresholds corresponding to thenumerical values c₂, c₁ and c₀ which indicate this coordinate values.

[0077] In a step a9, in a case where the threshold is smaller than thedensity information as the result in the step a8, the flow advances to astep a10. If the threshold is not smaller than the density information,the pixel for graphic drawing the coordinate values X and Y isdisregarded and the flow ends in a step a11.

[0078] In the step a10, the coordinate values X and Y are set as thepixel for performing a graphic drawing, thereafter, the flow ends in thestep a11.

[0079] In this embodiment, although the additional information of onebit is to be put on within an area corresponding to one threshold tableby switching two threshold tables, the present invention is not limitedto this manner. For example, the present invention includes the case forputting the additional information more than two bits on every areacorresponding to one threshold table by use of switching four or morethreshold tables.

[0080] In a second embodiment, an example of adding method for addingthe additional information in case of having a plurality of dots, whichgrow with the screening condition, within one threshold table will bedescribed. More particularly, the additional information is put byexecuting a process of switching the growing condition of a plurality ofdots at a level difficult to be perceived visually for each growing dotwithin one threshold table.

[0081] In a pseudo halftone processing which grows with the screeningcondition, a method for putting the additional information in a casewhere two or more growing dots are existed in one threshold table willbe described hereinafter.

[0082]FIGS. 6 and 7 indicates examples of threshold tables which growaround two dots within one threshold table as increasing the density.The growing condition of density of two dots in the threshold table arelittle different from each other when the case in FIG. 6 is comparedwith the case in FIG. 7. If the threshold table in FIG. 7 is comparedwith that in FIG. 6, especially, such a threshold table in FIG. 7 as thedensity of an upper left growing point within a dither matrix growspreferentially is prepared.

[0083] In this embodiment, the additional information is put byswitching the threshold tables in FIGS. 6 and 7 similar to the case inthe first embodiment. In case of using the threshold table in FIG. 6, 0is treated as a part (one bit) of the additional information (16 bits).In case of using the threshold table in FIG. 7, 1 is treated as a part(one bit) of the additional information (16 bits). The manner forputting the additional information by switching the threshold table issame as that in the first embodiment.

[0084] In this embodiment, in an area of high density, it is difficultto switch the threshold table, that is, it is difficult to detect theadditional information. Therefore, as in a description of the firstembodiment, a part of an image is not treated as the additional area,but an entire image is treated as the additional area, thereby enablingto switch the threshold table in an area of low density. That is, theadditional information can be detected.

[0085] However, if the entire image is treated as the additional area,an initial switching of the threshold table can not be performed. Thatis, an initial position of the additional information can not bedetermined. Therefore, in this embodiment, not only the additionalinformation but information (image) for indicating a reference positionused to notice the systematic positional relation is added. As a result,it becomes possible to analyze and extract the additional informationwithout mistaking the initial position of the additional information.

[0086]FIG. 8 indicates an assigning manner of blank areas used foradding information which indicates the reference position.

[0087] As shown in FIG. 8, areas in which the additional information isadded (additional areas) and the blank areas being the referencepositions for the additional areas are arranged to be adjoined eachother in their upper and lower sides.

[0088] The threshold table in FIG. 6 is unconditionally used for theblank area.

[0089] A size of the additional area is expressed as j×k. In thisembodiment, as in the first embodiment, each length of j and k hasdistance capable of containing four threshold tables corresponding tothe length of 32 pixels. Consequently, in this embodiment, since thethreshold tables of 4×4 pieces can be contained in each of theadditional areas, the additional information of 16 bits can be put. Itshould be noted that a size of the blank area is also expressed as j×kas apparent from FIG. 8.

[0090] In this embodiment, the combination of the threshold tables of8×8 pieces, which are structured by the blank areas and the additionalareas combined each other as shown in FIG. 9, is previously prepared.Consequently, an image processing corresponding to the coordinate valuesX and Y can be executed at a high speed. The coordinate position can beeasily discriminated by setting each parameter as a multiplier of 2.

[0091]FIG. 11 indicates the state of a bit column indicating acoordinate in each pixel of an image in the image processing unit,wherein a bit of the lowest order is represented by c₀ and a bit of themost upper order is represented by n₅.

[0092] In FIG. 11, three bits of the lowest order unit (c₂, c₁ and c₀)indicates a position of each of the additional areas, and such athreshold table as indicating the additional information of 16 bits onthe basis of information of four bits within six bits (n₅, n₄, n₃, n₂,n₁ and n₀) adjoining the three bits of the lowest order unit may have tobe selected.

[0093]FIG. 15 indicates the state of the threshold tables Q_(0.0) toQ_(3.3) of 16 pieces in each of the additional areas and the state ofexpressing the additional information of 16 bits by aligning each of bitinformation q_(0.0) to q_(3.3) represented by each of the thresholdtables.

[0094] As shown in FIG. 15, the threshold tables Q_(0.0) to Q_(3.3) areassigned to each of the additional areas. The threshold table shown inFIG. 6 or 7 is used for each of these tables Q_(0.0) to Q_(3.3).Therefore, the additional information of 16 bits is expressed byaligning the bit information q_(0.0) to q_(3.3) being the value of 0 or1 represented by the threshold tables Q_(0.0) to Q_(3.3).

[0095]FIG. 10 indicates a procedure for pseudo halftone processing apixel corresponded to coordinates X, Y.

[0096] In a step b2 in FIG. 10, at first, either the bit informationq_(x,y)=q_(0.0) to q_(3.3) (in case of additional area) or the bitinformation q=0 (in case of blank area) corresponding to the combinationof numerical values no to n₅ is read.

[0097] Next, in a step b3, it is judged whether the bit informationq_(x,y) is 1 or not. As the result of judgement, if the bit informationq_(x,y) is not 1, it is set to use the threshold table in FIG. 6 for thepixel of the coordinates X, Y (step b5). If the bit information q_(x,y)is 1, it is set to use the threshold table in FIG. 7 for the pixel ofthe coordinates X, Y (step b4).

[0098] In a step b6, the threshold corresponding to numerical values c₂,c₁ and c₀ is read from the threshold tables in the steps b4 and b5 tocompare it with a density value of the pixel of the coordinate values Xand Y.

[0099] In a step b7, if the threshold is smaller than densityinformation, the flow advances to a step b8 to set to perform a graphicdrawing of the coordinate values X and Y.

[0100] On the other hand, if the threshold is not smaller than thedensity information, it is set not to perform the graphic drawing of thecoordinate values X and Y to terminate the process.

[0101] As in the first embodiment, this embodiment enables to put aplurality of bit information on every little area by switching thresholdtables more than two pieces.

[0102] In a process for switching the threshold tables used in thesecond embodiment, a plurality of threshold tables have been preparedsubject to a plenty of areas of which density is comparatively in a lowlevel. Therefore, in a plurality of threshold tables used in the secondembodiment, it becomes impossible to discriminate the difference amongthe threshold tables if the density of an entire image becomes highlevel. A third embodiment solves this problem.

[0103] In the third embodiment, information of 0 or 1 is put on by useof switching threshold tables shown in FIGS. 12 and 13 instead of thethreshold tables shown in FIGS. 6 and 7 in the second embodiment. Sincethe other processes are same as those in the second embodiment, thedescription will be omitted. It should be noted that areas of obliquelines are such areas as both threshold tables have the same threshold.

[0104] In this embodiment, in a case where the density becomes highlevel (e.g., in a case where all pixels within the threshold table havethe density value of 240), in the threshold table in FIG. 12, a thicklinear square frame is remained as a white area. On the other hand, inthe threshold table in FIG. 13, a thick linear rectangle frame isremained as a white area. Accordingly, in this embodiment, in a casewhere a plenty of areas of which density is comparatively in a highlevel are existed, since the shape of white pixels remained in a matrixcan be recognized, the switching method of the threshold tables can beeasily analyzed.

[0105] Without limiting to the second and third embodiments, the presentinvention, in consideration of the second and third embodiments,includes a case for selectively using plural prepared threshold tableswhich can discriminate the switching method of the threshold tables(additional information) even if an image is in a high density or a lowdensity.

[0106] According to the above embodiments, in case of outputting aninputted multi-value image to a printer or the like after executing thepseudo halftone processing such as the dither processing or the like,since a predetermined additional information has to be added byswitching a processing method of this pseudo halftone processinggenerally executed, it becomes possible to add the additionalinformation, while preventing the deterioration of an image as long asit is possible. Especially, it is not required to add the dot patternfor expressing the additional information in another image processingunit after forming the pseudo halftone image, it becomes possible tosuppress the increasing of the cost of an apparatus and thedeterioration of the image caused by modulating an image after executingthe pseudo halftone processing can be prevented.

[0107] In the above embodiments, a case for executing the pseudohalftone processing by inputting only the multi-value image isdescribed. However, without limiting to this, the present inventionincludes a case for performing the above-mentioned processing to amulti-value image of each color component by inputting a multi-valuecolor image composed of a plurality of color components.

[0108] For example, in case of executing the pseudo halftone processingby inputting multi-value color image data composed of data of eight bitsof each color component yellow, magenta, cyan and black, a single pseudohalftone processing is executed to data of eight bits of each colorcomponent yellow, magenta, cyan and black (e.g., the pseudo halftoneprocessing is executed by using the threshold table in FIG. 1 to allcolor components). Thereafter, if the adding of the additionalinformation depending on the above-mentioned switching of the thresholdtables is performed to only a multi-value image expressed by data ofeight bits of yellow component, a color image having excellent qualitycan be formed and the additional information can be added.

[0109] The reason of adding the additional information to only theyellow component is that the yellow component, within the above fourcolor components, is a color most difficult to be perceived by humaneyes.

[0110] If the above-mentioned process is independently executed to eachof yellow, magenta, cyan and black components, four kinds of additionalinformation can be added. This process is not limited to the above colorcomponents, but may be applied to a multi-value color image composed ofR, G and B components or the like.

[0111] As described above, according to the present invention, since theadditional information is expressed by use of switching a plurality ofthreshold tables, it becomes possible to add the additional informationeffectively to an input image utilizing a general image processing.Therefore, the deterioration of an image after executing the generalimage processing can be remarkably prevented by adding the additionalinformation (changing of image data) in a final step.

[0112] Since the additional information is added by utilizing thegeneral image processing, an image processing is entirely executed at ahigh speed comparatively.

[0113] In a case where an image added the additional information isformed on a recording medium, the condition of forming this image(manufacturing number of an apparatus or the like) can be analyzed.

[0114] In a fourth embodiment, an example of applying the presentinvention to a laser beam printer (LBP) will be described. The presentinvention is not limited to the LBP but may be applied to, for example,another typed outputting apparatus such as an ink jet printer, a thermalprinter or the like.

[0115]FIG. 16 is a block diagram showing the structure of the LBP usedin the following embodiment.

[0116] In FIG. 16, print data which contains color multi-valueinformation described by a predetermined page description language (PDL)is inputted to an LBP 102 which can output a color image from anexternal device 101 such as a host computer or the like. A printercontroller 103 generates image data by analyzing the inputted printdata. A printer engine 105 prints an image, which is indicated by theimage data generated by the printer controller 103, on a recordingpaper. Keys and switches for instructing a desired operation to the LBP102 from an user and indicators such as a liquid crystal display (LCD),light emitting diodes (LED) and the like for displaying the operationcondition and the operation state of the LBP 102 are arranged on anoperation panel 104 which is an interface with the user.

[0117]FIG. 17 is a conceptional view showing a structural example of theLBP 102.

[0118] In FIG. 17, each mechanism for structuring the printer engine105, an engine control unit (not shown) for performing a controlconcerning a printing process depending on each mechanism and a holdingunit 203 for holding a control board in which the printer controller 103is structured are included in a body of equipment 201 of the LBP 102.

[0119] As each mechanism for structuring the printer engine 105, anoptical processing mechanism which forms a latent image on aphotosensitive drum 205 by scanning a laser beam, visualizes the latentimage and transfers the visualized image on the recording paper, afixing processing mechanism which fixes a toner image transferred on therecording paper, a feed processing mechanism of the recording paper anda carrying processing mechanism of the recording paper are provided.

[0120] A laser driver 206 of the optical processing mechanism performsan on/off driving of an output beam from a semiconductor laser element(not shown) on the basis of image data supplied from the printercontroller 103. The laser beam outputted from the semiconductor laserelement is scanned in the direction of an axis of the photosensitivedrum 205 (main scanning direction) by a rotational multi-mirrors 207.The laser beam reflected by the rotational multi-mirrors is guided tothe photosensitive drum 205 through a reflection mirror 208 to expose asurface of the photosensitive drum 205. The latent image, which isformed on the photosensitive drum 205 by an exposure scanning of thelaser beam, is visualized as a toner image by toners supplied from adevelopment unit 220. The development unit 220 supplies toners of eachcolor component Y (yellow), M (magenta), C (cyan) and K (black). Thetoner image on the photosensitive drum 205 is transferred to therecording paper which is carried in the direction of sub scanningsynchronized with a formation of an image of each color component by thefeed processing mechanism of the recording paper.

[0121] A detachable cartridge 204 holds the photosensitive drum 205 andthe development unit 220. The reflection mirror 208 is composed of asemi-transmittance type mirror of which back side has a beam detector209 arranged on it. The beam detector 209 detects the laser beam tosupply the detected signal to the printer controller 103. The printercontroller 103 generates a horizontal synchronization signal fordetermining an exposure timing on the basis of the detected signal inthe beam detector 209. The horizontal synchronization signal is suppliedto each part of the printer engine 105 as a synchronization signal.

[0122] A fixing unit 216 in the fixing processing mechanism heats andpressures the toner image transferred on the recording paper to fix iton the recording paper. A heater for heating the toner image iscontrolled by an engine control unit so as to obtain the predeterminedfixing temperature.

[0123] The feed processing mechanism of the recording paper has acassette 210 for holding recording papers and a manual feeding tray 219and is structured to selectively feed the recording paper in thecassette 210 or the manual feeding tray 219. In the cassette 210equipped in the body of equipment 201, a recording paper size detectionmechanism for detecting the size of recording papers in accordance witha moving position of a partition plate (not shown) is provided. Therecording papers held in the cassette 210 are carried one by one to apaper feed roller 212 in response to the rotational driving of acassette feed clutch 211. The cassette feed clutch 211 is composed of acam which is intermittently rotated every feeding of the recording paperby a driving unit (not shown). One recording paper is fed to the paperfeed roller 212 every rotating of the cam.

[0124] The paper feed roller 212 carries the recording paper until sucha position as a leading edge of the recording paper reaches to a resistshutter 214. The resist shutter 214 is used for coinciding a leadingedge of the toner image formed on the photosensitive drum 205 with avicinity of the leading edge of the recording paper which is to be fed.On the other hand, recording papers in the manual feeding tray 219 aresupplied to the resist shutter 214 by a paper feed roller 215.

[0125] The carrying processing mechanism of the recording paper has acarrying roller 213 for carrying recording papers released from theresist shutter 214 to the photosensitive drum 205, carrying rollers 217and 218 for guiding the recording papers discharged from the fixing unit216 to a discharging tray provided on an upper portion of the body ofequipment 201 and a driving unit (not shown) for driving the carryingrollers 213, 217 and 218.

[0126]FIG. 18 is a block diagram showing a structural example of theprinter controller 103.

[0127] The printer controller 103 has a host interface 302 which has aninput buffer (not shown) for momentarily storing the print data inputtedfrom the external device 101 and an output buffer (not shown) formomentarily storing a signal which is to be transmitted to the externaldevice 101. The host interface 302 composes an input/output unit forinputting and outputting a signal which is communicated between the hostinterface 302 and the external device 101 and controls a communicationtherebetween.

[0128] The print data inputted through the host interface 302 issupplied to an image data generation unit 303. The image data generationunit 303 analyzes the print data on the basis of a predeterminedanalyzing procedure. As this analyzing, for example, there has beenknown a PDL analyzing process. The image data generation unit 303produces image data which can be processed by the printer engine 105 onthe basis of the analyzed result.

[0129] More particularly, the PDL analyzing process is such a process asanalyzing the print data and produces object information on the basis ofthe analyzed result. A rasterizing process, the pseudo halftoneprocessing or the like is sequentially executed simultaneously with thegenerating of the object information. The rasterizing process includes aprocess for converting data of R, G and B contained in the print datainto data of Y, M, C and K which can be processed by the printer engine105 and a process for converting character codes contained in the printdata into font data such as pre-stored bit patterns, an outline font orthe like. Further, in the rasterizing process, bit map data is producedwith a band unit of predetermined width and the pseudo halftoneprocessing such as the dither processing, an error diffusion processingor the like is executed to the bit map data of band unit to generateimage data which can be printed.

[0130] The image data generated in this manner is stored in an imagememory 305. The image data stored in the image memory 305 is read out bya DMA control unit 308 of which operation follows an instruction from aCPU 309.

[0131] The image data which is read out from the image memory 305 istransferred to the printer engine 105 as a video signal through anengine interface 306. The engine interface 306 has an output buffer (notshown) for momentarily storing the video signal which is to betransmitted to the printer engine 105 and an input buffer (not shown)for momentarily storing a signal transmitted from the printer engine105. The engine interface 306 composes an input/output unit forinputting and outputting a signal which is communicated between theengine interface 306 and the printer engine 105 and controls acommunication therebetween.

[0132] A panel interface 301 constitutes an interface between anoperation panel 104 and the CPU 309. A setting instruction or the likeconcerning an operation mode of a printer inputted from the operationpanel 104 is inputted to the CPU 309 through the panel interface 301 anda system bus 311.

[0133] The CPU 309 controls the above-mentioned each block in accordancewith a control program stored in a ROM 304 on the basis of theinstructions from the operation panel 104 and the external device 101.The control program stored in the ROM 304 is constituted by an operatingsystem (OS) for performing a time-divisional control with a unit of loadmodule called as task by a system clock and a plurality of load modulescontrolled with a unit of function by this OS. The control program whichincludes the load modules is stored in a non-volatile memory 310 such asan EEPROM in accordance with a requirement. The CPU uses a RAM 307 as awork area of calculating processes.

[0134] Each block including the above-mentioned CPU 309 is mutuallyconnected through the system bus 311 composed of an address bus and adata bus.

[0135]FIG. 19 is a flow chart showing an example of a procedure forgenerating the video signal by the printer controller 103 andtransmitting it.

[0136] When the print data is inputted to the printer controller 103from the external device 101, the process is executed to generate theobject information for performing a graphic drawing. The PDL analyzingprocess is continued as long as input data is existed for continuouslygenerating the object information.

[0137] The rasterizing process shown in FIG. 19 is executedsimultaneously with a generation process for generating this objectinformation. In a step S401, a preparation process for transferring datato the printer engine 105 is executed before executing the rasterizingprocess. In this preparation process, a designation of formation color,a designation of toner density and other designations are performed forthe printer engine 105. In this embodiment, the designation of formationcolor is performed in the order of M, C, Y and K. The designating orderof the forming color depends on the printer engine 105.

[0138] In a step S402, the rasterizing process is executed on the basisof the generated objection information and band data of a predeterminedline width is generated. In a step S403, if it is confirmed that theband data of one band is generated, the pseudo halftone processing usinga dither pattern corresponding to the formation color is executed in astep S404. The video signal corresponding to the forming color istransmitted to the printer engine 105 in a step S405.

[0139] Next, in a step S406, it is judged whether a data processingcorresponding to the forming color for one page is terminated or not. Ifit is not terminated, the flow returns to the step S402 and the processfrom the step S402 to the step S405 is repeated until terminating thedata processing corresponding to the forming color for one page.

[0140] In a case where the data processing corresponding to the formingcolor for one page is terminated, it is judged whether the dataprocessing corresponding to all of colors M, C, Y and K is terminated ornot in a step S407. If it is not terminated, the flow returns to thestep S401 and the process from the step S401 to the step S406 isrepeated until terminating the data processing corresponding to fourcolors. When the data processing corresponding to four colors isterminated, the process in the flow is terminated.

[0141]FIG. 20 is a flow chart showing an example of the processingprocedure for adding the additional information used for chasing theforgery. This process, which corresponds to the process in the step S404in FIG. 19, is executed by the CPU 309.

[0142] In this embodiment, an adding method for adding the additionalinformation is switched in accordance with the kind of suppliedrecording medium. It is assumed that, especially, the additionalinformation is only put on a specific recording medium by switching thethreshold tables in performing of the pseudo halftone processing. Theswitching method of the threshold tables is fundamentally same as thatin the above-mentioned first to third embodiments. The additionalinformation is added by performing a modulation for adding apredetermined value to an image signal of a color component which is themost difficult to be perceived by human eyes (e.g., yellow) within colorcomponents (e.g., C, M, Y and K) of an output image.

[0143] In a step S501 in FIG. 5, it is examined whether color data to beprocessed is data of color component to which the additional informationis added. If it is not, the pseudo halftone processing by means of thegeneral dither processing is executed in a step S503.

[0144] In case of the data of color component to which the additionalinformation is added, the kind of recording medium to be supplied isexamined in a step S502. If it is an OHT (Overhead Transparency) being atransparent recording medium used for an overhead projector, the pseudohalftone processing using two kinds of the threshold tables to expressthe additional information is executed in a step S504 in order toprevent prominence of the additional information. That is, only in caseof the OHT, the additional information is added by such a method asdescribed in each of the first to third embodiments. If the recordingmedium to be supplied is not the OHT, the additional information isadded by executing the general pseudo halftone processing in the stepS503 and sequentially performing the conventionally known one of theadding methods, that is, which is a modulation for merely adding thepredetermined value to an image after executing the pseudo halftoneprocessing, in a step S506. The same pseudo halftone processing isexecuted in steps S503 and S505.

[0145] In this manner, the CPU 309 selects an appropriate adding methodfor adding the additional information in accordance with the kind ofrecording medium to be supplied. The kind of recording medium may bejudged by an output signal from a light transmission type sensor or alight reflection type sensor (not shown) in the vicinity of the resistshutter 214.

[0146] A technique for executing the pseudo halftone processing by usingtwo kinds of threshold tables so as to put the additional information,that is, the technique for putting the additional information byexpressing information depending on the switching method of the twokinds of the threshold tables will be described. In a screening process,as in the first to third embodiments, it is assumed that one of thevalues 0 to 255 is inputted as a gradation value by treating a pixelblock composed of 8×8 pixels as a processing unit.

[0147] In this embodiment, only in case of recording an image on theOHT, the additional information is added to this image by switching thethreshold tables used for producing a pseudo halftone image. That is,the pseudo halftone image having different pixel growing patterns isformed by switching the threshold tables in FIGS. 21 and 22 used forproducing the pseudo halftone image (image after performing the ditherprocessing) so that the additional information is indicated.Consequently, by analyzing the switching manner of the threshold tables,from the pseudo halftone image formed on the OHT, the additionalinformation which is put on this image can be extracted.

[0148] It is assumed that each of the threshold tables shown in FIGS. 21and 22 has the size of 8×8 pixels and the dither processing issequentially executed to the inputted image data. In this embodiment, ina case where the threshold table shown in FIG. 21 is used, 0 isindicated. In a case where the threshold table shown in FIG. 22 is used,1 is indicated. Accordingly, the additional information of one bit canbe put on every area of 8×8 pixels in an image. In this embodiment, ifthe additional information to be added is data of 16 bits, an areacorresponding to the threshold tables of 16 pieces is required. Itshould be noted that an expressing manner of the additional informationis not limited to this manner, but may be expressed, without treatingone bit information of 0 or 1 indicated by the threshold tables shown inFIGS. 21 and 22 as a part of the additional information as it is, by themanner of run-length using 0 and 1. On the other hand, in thisembodiment, an area for putting the additional information on an imageof one frame is not treated as an entire image, but an additional area(area for switching the threshold tables shown in FIGS. 21 and 22) is tobe assigned at a fixed period. However, the present invention is notlimited to this, but the additional area may be assigned to an entireimage.

[0149] Next, the state of assigning manner of the above-mentionedadditional area in this embodiment is shown in FIG. 23. In FIG. 23,areas of oblique lines are additional areas. That is, the additionalinformation (in this embodiment, 16 bits) has to be put on these areasby switching the threshold tables shown in FIGS. 21 and 22. Theadditional area has the size of containing j×k threshold tables (in thisembodiment, j=4 and k=4). That is, each of the additional areas canexpress the additional information of j×k bits. As to the positionalrelation of each area among the additional areas, it is assumed thatlength m and length n in FIG. 23 have distance capable of containing thethreshold tables of 16 pieces (8×16 pixels).

[0150]FIG. 24 indicates the state of a bit column indicating acoordinate in each pixel of an image in the image processing unit. Asmentioned above, by setting each parameter as a multiplier of 2, acoordinate value expressed in binary number can be easily treated asshown in FIG. 24. In FIG. 24, three bits of the lowest order unit (c₂,c₁, c₀) is the coordinate indicating a position within each of thethreshold tables. When two bits of upper order (n₃, n₂) within four bits(n₃, n₂, n₁, n₀) adjoining the three bits of the lowest order unitcorresponds to specific values (in this embodiment, n₃=1, n₂=1), sincesuch a threshold table as indicating the additional information of 16bits may have to be selected, it becomes possible to perform ahigh-speed processing. In this embodiment, the threshold table shown inFIG. 21 is unconditionally used to an area other than areas of obliquelines (additional areas) shown in FIG. 23.

[0151]FIG. 25 indicates the state of threshold tables of 16 piecesQ_(0.0) to Q_(3.3) in each of the additional areas and the state of theadditional information is expressed by aligning each of bit informationq_(0.0) to q_(3.3) represented by each of the threshold tables. As shownin FIG. 25, the threshold tables Q_(0.0) to Q_(3.3) are assigned to eachof the additional areas. The threshold table shown in FIG. 21 or 22 isused for each of these tables Q_(0.0) to Q_(3.3). Therefore, theadditional information is expressed by aligning the bit informationq_(0.0) to q_(3.3) being the value of 0 or 1 represented by thethreshold tables Q_(0.0) to Q_(3.3).

[0152]FIG. 26 indicates a procedure for pseudo half processing a pixelcorresponded to coordinates X, Y. In a step a2, as to a coordinate valueX, it is judged whether each of n₃ and N₂ is 1 or not. If each of n₃ andn₂ is not 1, the flow advances to a step a7. If each of n₃ and n₂ is 1,the flow advances to a step a3. Next, in the step a3, as to a coordinatevalue Y, it is judged whether each of n₃ and n₂ is 1 or not. If each ofn₃ and n₂ is not 1, the flow advances to the step a7. If both of n₃ andn₂ are 1, the flow advances to a step a4. In the step a4, either of bitinformation q_(0.0) to q_(3.3) corresponding to numerical values n₁ andn₀ of the coordinate values X and Y are read. In a step a5, it is judgedwhether the bit information q_(0.0) to q_(3.3) which are read are 1 ornot. If the judged result does not obtain 1, the flow advances to thestep a7. If the judged result obtains 1, the flow advances to a step a6.

[0153] In the step a6, it is set to perform the pseudo halftoneprocessing by using the threshold table shown in FIG. 22, that is, thetable of indicating 1. On the other hand, in the step a7, it is set toperform the pseudo halftone processing by using the threshold tableshown in FIG. 21, that is, the table of indicating 0. In a step a8,density information (pixel value) of the coordinate values X and Y iscompared with the thresholds corresponding to the numerical values c₂,c₁ and c₀ which indicate this coordinate values. In a step a9, in a casewhere the threshold is smaller than the density information as theresult in the step a8, the flow advances to a step a10. If the thresholdis not smaller than the density information, the pixel for graphicdrawing the coordinate values X and Y is disregarded and the flow endsin a step a11. In the step a10, the coordinate values X and Y are set asthe pixel for performing a graphic drawing, thereafter, the flow ends inthe step a11.

[0154] In this embodiment, in case of recording an image on the OHT,although the additional information of one bit is to be put on within anarea corresponding to one threshold table by switching two thresholdtables, the present invention is not limited to this manner. Forexample, the present invention includes the case for putting theadditional information more than two bits on every area corresponding toone threshold table by use of switching four or more threshold tables.

[0155] Although the adding method for adding the additional informationas in the first to third embodiments is especially used only when imagedata is recorded on the OHP, the above-mentioned process may be executedonly when the image data is recorded on a coated paper.

[0156] In the above description, because of a high-speed processing, thevalues of 2^(n) (n: positive integer) are used as various parameters soas to realize various judgements by cutting out the bits. However, thevalues of positive integer can be used as these values if permitting theloss of time used for a calculating process.

[0157] Further, in the above description, an example of preparing onlythe two threshold tables used in case of executing the pseudo halftoneprocessing is described. However, it becomes possible to put theadditional information by shifting each of growing dots of pixels in thedifferent direction.

[0158] In this manner, according to this embodiment, for example, incase of forming an image on a specific recording medium such as the OHT,the additional information is added by putting the additionalinformation depending on the switching manner of the threshold tableswhich indicate the growing patterns of screen aiming at the screeningprocess in a pseudo halftone expression. As a result, the additionalinformation can be added by a method according to the kind of recordingmedium and the deterioration of quality of an output image can beprevented, while maintaining the detectability of the additionalinformation.

[0159] In the following, an image processing apparatus in a fifthembodiment according to the present invention will be described. In thisembodiment, the same structure as that in the fourth embodiment has thesame reference numeral and the description thereof will be omitted.

[0160]FIG. 27 is a flow chart showing an example of the procedure forgenerating a video signal by the printer controller 103 and transmittingit. The same processing step as that in the flow chart shown in FIG. 19has the same reference numeral and the description thereof will beomitted. In a step S701, it is judged whether it is a forming color, towhich the additional information is added, or not after executing thepseudo halftone processing in the step S404. In case of the formingcolor, a forming pattern of the additional information is selected in astep S702 and a process for adding the additional information dependingon the selected forming pattern is executed in a step S703. In the stepS701, if it is judged that it is not the forming color to which theadditional information is added, a process in the step S405 is executed.

[0161]FIG. 28 is a flow chart showing an example of the procedure, whichcorresponds to the process in the step S702, for selecting theadditional information in accordance with a characteristic of recordingmedium.

[0162] In the step S501, the characteristic of recording medium suppliedfrom the paper feeding cassette 210 or the manual feeding tray 219 isanalyzed. That is, as in an example shown in FIG. 29, the ROM 304 or theEEPROM 310 stores a table in which data indicating the characteristic ofrecording medium is registered. The characteristic of recording mediumcan be analyzed by comparing the data stored in this table with anoutput from a sensor. Here, if a fixing characteristic is explained, therecording medium has various kinds of papers such as a plain paper, aspecial purpose paper, a second base paper, a card or the like and thefixing characteristic of a toner becomes different condition due to acharacteristic of surface of a paper. Since the reflection of lightbecomes different condition due to the characteristic of surface of thepaper, if data indicating the reflection condition of light is stored inthe table, the characteristic of supplied recording medium can beanalyzed by the output signal from the sensor.

[0163] The kind of supplied recording medium is judged in the step S502on the basis of the characteristic of recording medium analyzed in thestep S501. For example, in a case where the recording medium is judgedas the card, since the supplied recording medium has an inferior fixingcharacteristic of the toner, the additional information used for chasingthe forgery becomes difficult to be detected. Therefore, it is requiredto select a forming pattern of remarkable additional information tomaintain the detectability. Accordingly, in the step S503, a formingpattern of the most suitable additional information is selected inaccordance with the kind of judged recording medium.

[0164]FIGS. 30 and 31 indicate corresponded examples between the kindsof recording medium and forming patterns of the additional information.For example, in case of the card, as shown in FIG. 30, a fixingcharacteristic of F_level corresponds to 3 and a forming pattern of theadditional information of F_pattern 3, which corresponds to the samelevel as that in the fixing characteristic, is selected. That is, sincethe forming pattern of the additional information, which is used forchasing the forgery, is difficult to be fixed on the recording mediumhaving the inferior fixing characteristic such as the card, a largeforming pattern is selected.

[0165] On the contrary, in a case where the recording medium is judgedas the recording medium having a superior fixing characteristic of thetoner such as the special purpose paper, of which fixing characteristicof F_level corresponds to 0, a forming pattern of F_pattern 0corresponding to F_level 0 is selected in order to suppress thedeterioration of image quality by reducing the level of forming patternof the additional information.

[0166] In a case where the recording medium is judged as the recordingmedium having a high transmittance such as the second base paper, asshown in FIG. 31, transmittance of P_level corresponds to 0 and aforming pattern of the additional information of P_pattern 0, whichcorresponds to the same level as that in the transmittance, is selected.That is, since the additional information, which is used for chasing theforgery, becomes remarkable on the recording medium having the hightransmittance such as the second base paper, the quality of an outputimage is deteriorated. Therefore, the forming pattern of the additionalinformation, which is not remarkable, is selected.

[0167] In a case where the recording medium is judged as the recordingmedium having a comparatively low transmittance such as the specialpurpose paper of which transmittance of P_level corresponds to 2, aforming pattern of the additional information of P_pattern 2corresponding to P_level 2 is selected in order to select and add thepattern of the additional information which is difficult to be detected.

[0168] As to the F_pattern and the P_pattern, of which priority may bepreviously set to select the F_pattern or the P_pattern. Besides, it maybe set in accordance with a result of recognizing an image which is tobe formed on the recording medium. As a result of recognizing an image,as similarity between an image to be formed and an image of a specificoriginal prohibited to copy becomes closer, it may be set that adetectable forming pattern is prior to other patterns.

[0169] Of course, various analyzing items and various forming patternsof the additional information concerning the recording medium may beoptionally set. That is, the present invention is not limited to suchtables as shown in FIGS. 29, 30 and 31.

[0170] As described, according to the present invention, it becomespossible to select and add a forming pattern of the suitable additionalinformation which responds to the judged kind of recording medium byjudging the kind of recording medium under analyzing of thecharacteristic of recording medium to be supplied.

[0171] In each of the above-mentioned embodiments, although an exampleof selecting the forming pattern of the additional information isdescribed, as to an adjustment of the forming pattern, there fonds suchadjustments as changing an additional form of the forming pattern,changing an adding method of the forming pattern, changing additionaldensity of the forming pattern and changing a color of development agentused for adding the forming pattern. For example, in a case where it isjudged that the characteristic of recording medium to be supplied is aninferior fixing characteristic, if the additional density of formingpattern of the general additional information maintains a level of tenpercent, such a process as increasing the additional density to fiftypercent can be executed in order to maintain the detectability of theadditional information.

[0172] It should be noted that the present invention is not limited tothe above-mentioned embodiments, but may be applied to a system composedof a plurality of devices (e.g., host computer, interface unit, reader,printer or the like) or to an apparatus composed of one device (e.g.,copying machine, facsimile apparatus or the like).

[0173] It is needless to say that an object of the present invention isattained by supplying a storing medium which stores a program code ofsoftware to realize the functions in the above-mentioned embodiments toa system or an apparatus, and also the system or a computer (CPU or MPU)in the apparatus reads out the program code stored in the storing mediumto execute it. In this case, the program code itself, which is read outfrom the storing medium, realizes the functions in the above-mentionedembodiments, and the storing medium which stores the program codeconstitutes the present invention. As the storing medium for supplyingthe program code, for example, a floppy disk, a hard disk, an opticaldisk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-R/W, a DVD-ROM, aDVD-RAM, a magnetic tape, a non-volatile memory card, a ROM or the likecan be used.

[0174] Also, it is needless to say that the present invention includesnot only the case for realizing the functions in the above-mentionedembodiments by executing the program code which is read out by thecomputer but the case for realizing the functions in the above-mentionedembodiments by such a process as an OS (operating system) or the likeoperated in the computer executes all or a part of an actual processingon the basis of an instruction of the program code.

[0175] Further, it is needless to say that the present inventionincludes the case for realizing the functions in the above-mentionedembodiments by such a process as a CPU or the like provided in afunction expanding card or a function expanding unit executes all or apart of the actual processing on the basis of an instruction of theprogram code after the program code which is read out from the storingmedium is written in a memory provided in the function expanding cardinserted to the computer or the function expanding unit connected to thecomputer.

[0176] As described above, according to the present invention, since aprocessing method in the pseudo halftone processing used for a generalimage formation is to be selected by a switching method according to theadditional information, as a result, the switching process itselfbecomes to put the additional information. Consequently, it is notrequired to provide specific adding means for adding the additionalinformation.

[0177] The present invention can be modified in various manner, withinthe scope of the following claims.

What is claimed is:
 1. An image processing apparatus comprising: inputmeans for inputting M-value image data; and N-value generation means forconverting the M-value image data inputted by said input means intoN-value image data on the basis of threshold table groups composed ofplural kinds of threshold tables of which using order is determined soas to indicate predetermined additional information, wherein the value Mis larger than the value N.
 2. An apparatus according to claim 1 ,wherein the M-value image data is 256-value image data.
 3. An apparatusaccording to claim 1 , wherein the N-value image data is binary imagedata.
 4. An apparatus according to claim 1 , wherein the threshold tableis used for a dither processing and said N-value generation meansconverts the M-value image data into the N-value image data by executingthe dither processing.
 5. An apparatus according to claim 1 , whereinthe apparatus further comprises printing means for printing the N-valueimage data obtained by the conversion performed by said N-valuegeneration means.
 6. An apparatus according to claim 5 , wherein saidprinting means is an ink jet printer.
 7. An apparatus according to claim5 , wherein said printing means is a laser beam printer.
 8. An apparatusaccording to claim 1 , wherein the apparatus further comprises readingmeans for reading an original to generate the M-value image data.
 9. Anapparatus according to claim 1 , wherein each of the plural kinds ofthreshold tables is a dither matrix having a size of m×n pixels and theplural kinds of threshold tables are different from each otherconcerning the construction of thresholds of m×n pieces which constructthe dither matrix.
 10. An apparatus according to claim 1 , wherein theM-value image data contains a plurality of color components and saidN-value generation means converts the M-value image data into theN-value image data for only one color of the plural color components onthe basis of the threshold table groups composed of the plural kinds ofthreshold tables.
 11. An apparatus according to claim 1 , wherein theapparatus further comprises detection means for detecting the kind of arecording medium on which an image indicated by the M-value image datainputted by said input means is to be formed, wherein said N-valuegeneration means controls whether the N-value generation is performed ornot to the M-value image data on the basis of the threshold table groupsin accordance with the kind of the recording medium.
 12. An apparatusaccording to claim 11 , wherein said N-value generation means performsthe N-value generation to the M-value image data on the basis of thethreshold table groups in a case where the recording medium is an OHP(Over Head Transparency).
 13. An image processing method comprising thesteps of: inputting M-value image data; and converting the M-value imagedata inputted in said input step into N-value image data on the basis ofthreshold table groups composed of plural kinds of threshold tables ofwhich using order is determined so as to indicate predeterminedadditional information, wherein the value M is larger than the value N.14. A storing medium which stores an image processing program in areadable state of reading out it from a computer, wherein the imageprocessing program comprising the steps of: inputting M-value imagedata; and converting the M-value image data inputted in said input stepinto N-value image data on the basis of threshold table groups composedof plural kinds of threshold tables of which using order is determinedso as to indicate predetermined additional information, wherein thevalue M is larger than the value N.